1. Field of the Invention
The present invention relates a switching converter and related control method, and more particularly, to a switching converter capable of immediately monitoring total energy of inductor and flexibly performing energy distribution and related control method.
2. Description of the Prior Art
DC/DC converter is mainly utilized for adjusting voltage levels (boost or buck) such that the voltage levels are stable at set voltage for providing operation voltages required by the electronic device. A single inductor multiple output (SIMO) switching converter can provide multiple different output voltages via a structure of single inductor. Therefore, the SIMO switching converter is suitably for portable electronic devices or system-on-chips. Please refer to FIG. 1, which is a schematic diagram of a conventional SIMO switching converter 10. As shown in FIG. 1, an inductor 100 receives an input voltage VI through an input end IN for storing energy. Via a charging switch SW0 and output switches SW1-SW4 controlled by a control circuit 102, the energy stored in the inductor 100 are distributed to output capacitors CO1-CO4, respectively, for providing output voltage signals VO_1-VO_4 to loads Load1-Load4 through output ends OUT1-OUT4. In other words, the SIMO switching converter 10 can respectively provide the output voltage signals VO_1-VO_4 to the loads Load1-Load4. In short, the SIMO switching converter 10 can store energy from a voltage source and further distribute the stored energy for providing multiple output voltage signals.
The operation modes of the SIMO switching converter 10 are mainly classified into a charging/discharging mode and an energy distribution mode. The charging/discharging mode represents the charging or discharging operations of the inductor 100. The energy distribution mode represents the energy distribution operations of the energy stored in the inductor 100. In the charging/discharging mode, the inductor 100 performs the charging or discharging operations, and an inductor current of the inductor 100 is accordingly increased or decreased. In the energy distribution mode, various energy distribution operations can be performed according to requirements of applications. For example, when the SIMO switching converter 10 is utilized in a buck mode, the SIMO switching converter 10 can store energy in the inductor 100 and distribute the energy stored in the inductor 100 at the same time. Or, when the SIMO switching converter 10 is utilized in a boost mode, the SIMO switching converter 10 can store energy in the inductor 100 for a certain time and distribute the energy stored in the inductor 100 in the energy distribution mode.
The charging switch SW0 and output switches SW1-SW4 are controlled by the control circuit 102 in both the charging/discharging mode and the energy distribution mode, for outputting the energy stored in the inductor 100 to each load. Generally, the control circuit 102 controls each switch via different modulation methods in a fixed operational frequency. For example, common fixed frequency controls comprise the bang-bang control (or the hysteresis control) and the pulse width modulation control. Please refer to FIG. 2, which is a schematic diagram of an SIMO switching converter 20 using the bang-bang control. Different from FIG. 1, the SIMO switching converter 20 includes a control circuit 202 adapting the bang-bang control. The control circuit 202 includes voltage scalers VS1-VS4, comparators COM1-COM4 and a logic control unit 204. The voltage scalers VS1-VS4 are coupled to output ends OUT1-OUT4, for receiving output voltage signals VO_1-VO_4. As shown in FIG. 2, the comparator COM1 generates a comparing signal SP_1 to the logic control unit 204 according to the signal outputted by the voltage scaler VS1 and a reference voltage signal Vref. Similarly, the comparator COM2-COM4 respectively generate comparing signals SP_2-SP_4 according to the signals outputted by the voltage scalers VS2-VS4 and the reference voltage Vref. The logic control unit 204 generates charging control signal SC_0 and output control signals SC_1-SC_4 according to the comparing signals SP_1-SP_4, for controlling the charging switch SW0 and the output switches SW1-SW4. In other words, the operations of charging/discharging and energy distribution of the SIMO switching converter 20 are determined by controlling the conducting sequence of the charging switch SW0 and the output switches SW1-SW4. In detail, the control circuit 202 utilizes the comparators COM1-COM4 and the logic control unit 204 for determining whether the total energy stored in the inductor 100 is too high or too low (in the charging/discharging mode), and distributing the energy to the output ends OUT1-OUT4 to provide output voltage signals VO_1-VO_4 (in the energy distribution mode). Since the comparator can be regarded as an amplifier with high gain, the comparators COM1-COM4 can rapidly adjust the comparing signals SP_0-SP_4 when the loads Load1-Load4 have different load variations. As a result, the control circuit 202 adapting the bang-bang control rapidly reflects the load status. However, rapid reflection for the load status results in problems such as misoperations, huge output voltage ripple, and huge ripple on the current of the inductor 100.
Please refer to FIG. 3, which is a schematic diagram of a conventional SIMO switching converter 30 using the pulse width modulation control. Different from FIG. 2, a control unit 302 configures an error amplifier EA, a pulse width modulator 304 and a capacitor C for detecting the energy distributed to the output voltage signal of the last stage, to determine the total energy required by the inductor 100 in the charging/discharging mode. The pulse width modulator 304 generates a comparing signal SP_5 to the logic control unit 204 according to an error voltage signal Ve outputted by the error amplifier EA and an inductor voltage signal Vsen. Please refer to FIG. 4, which is a schematic diagram of the pulse width modulator 304 shown in FIG. 3. The pulse width modulator 304 includes a comparator COM and an adder 402. The adder 402 pluses an inductor voltage signal Vsen and a triangular wave signal Va for generating a ramp signal Vramp. The comparator COM compares the error voltage signal Ve and the ramp signal Vramp and accordingly generates the comparing signal SP_5. A flying wheel switch SW_F coupled across the inductor 100 is utilized for controlling the continuous conducting mode of the SIMO switching converter 30. Please jointly refer to FIG. 3 and FIG. 4, when the energy acquired by the output voltage signal VO_4 is low, the error voltage signal Ve outputted by the error amplifier Ea is increased. As a result, the duty ratio of the comparing signal SP_5 outputted by the comparator 402 is accordingly increased. In such a condition, the logic control unit 204 accordingly generates related control signals for storing more energy to generate related output voltage signals, to regulate the output voltage signals. In other words, the control circuit 402 sets the priority of the output voltage signal VO_4 to a lowest priority, and the pulse width modulator 304 provides the corresponding comparing signal SP_5 to the logic control unit 204 when the energy of the voltage signal VO_4 is insufficient. The logic control unit 204 then accordingly prolongs the conducting time of the corresponding switch for prolonging charging time of the inductor 100, to achieve the goal of controlling the charging/discharging mode.
The SIMO switching converter 30 shown in FIG. 3 uses the bang-bang control in the energy distribution mode, and uses the pulse width modulation control in the charging/discharging mode for determining the total energy required by the inductor 100 in the charging/discharging mode. However, since the charging/discharging mode is determined by the output signal with the lowest priority (i.e. the output voltage VO_4) and the output voltage signal with the lowest priority can only acquire remaining energy, the voltage signal with the lowest priority can not reflect current status to the output stages with higher priority and the reaction time of the inductor current would be slower.
On the other hand, please refer to FIG. 5, which is a schematic diagram of a SIMO switching converter 50 using the pulse width modulation control. Different from FIG. 3, the SIMO switching converter 50 utilizes the pulse width modulation control on all the output paths. In other words, the SIMO switching converter 50 adapts the pulse width modulation control in both the charging/discharging mode and the energy distribution mode. A control circuit 502 includes error amplifiers EA_1-EA_4, capacitors C1-C4, switches SW_P1-SW_P4, a phase controller 504 and a pulse width modulator 506. The SIMO switching converter 50 realizes the time multiplexed control via the phase controller 504 controls the switches SW_P1-SW_P4, to achieve the charging/discharging control and energy distribution. However, since utilizing the time multiplexed control, there are multiple times of the charging/discharging mode in a time period. In such a condition, the switching times of the switches increases such that the switching loss increases. In addition, the SIMO switching converter 50 using the pulse width modulation control on both charging/discharging mode and the energy distribution mode results in limiting the maximum operation frequency and the flexibility of structure extension.
In brief, for the switching converter using the structure of providing multiple different output voltages via an inductor, how to immediately determines the charging time of the inductor and flexibly distribute energy should be a focus in progressive circuit design.